U.S. patent number 11,266,023 [Application Number 16/384,327] was granted by the patent office on 2022-03-01 for electronic circuit production.
This patent grant is currently assigned to DST Innovations Limited. The grantee listed for this patent is DST Innovations Limited. Invention is credited to Anthony Miles, Robert Miles.
United States Patent |
11,266,023 |
Miles , et al. |
March 1, 2022 |
Electronic circuit production
Abstract
Electrolytic Etching/Deposition System. A system for continuous
circuit fabrication comprising means for storing and dispensing the
substrate, means for laminating the substrate, means for printing
the substrate, means for optical inspection of the substrate, means
for photolithography of the substrate, means for drying the
substrate, means for developing the substrate, means for washing
the substrate and means for electroplating the substrate.
Inventors: |
Miles; Anthony (Bridgend,
GB), Miles; Robert (Bridgend, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
DST Innovations Limited |
Bridgend |
N/A |
GB |
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Assignee: |
DST Innovations Limited
(Bridgend, GB)
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Family
ID: |
1000006142787 |
Appl.
No.: |
16/384,327 |
Filed: |
April 15, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190246503 A1 |
Aug 8, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15023307 |
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PCT/GB2014/052865 |
Sep 19, 2014 |
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Foreign Application Priority Data
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Sep 19, 2013 [GB] |
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1316652 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D
17/00 (20130101); C25F 7/00 (20130101); H05K
3/07 (20130101); C25D 7/00 (20130101); H05K
3/068 (20130101); C25D 7/0628 (20130101); H01L
21/3063 (20130101); C25F 3/02 (20130101); C25D
5/34 (20130101); C25D 7/0657 (20130101); C25D
9/08 (20130101) |
Current International
Class: |
C25D
7/06 (20060101); C25D 17/00 (20060101); C25D
7/00 (20060101); C25D 5/34 (20060101); H05K
3/07 (20060101); C25D 3/34 (20060101); C25F
7/00 (20060101); C25F 3/02 (20060101); H01L
21/3063 (20060101); H05K 3/06 (20060101); C25D
9/08 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10 2005 031948 |
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Jun 2006 |
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DE |
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1 390 709 |
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Apr 1975 |
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GB |
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2 072 704 |
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Oct 1981 |
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GB |
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H01-291992 |
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Nov 1989 |
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JP |
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H04-268084 |
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Sep 1992 |
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JP |
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2004-131842 |
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Apr 2004 |
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JP |
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2005-166977 |
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Jun 2005 |
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JP |
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2011-021233 |
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Feb 2011 |
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JP |
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Other References
International Search Report of the International Searching
Authority dated Feb. 24, 2015, issued in connection with
International Application No. PCT/GB2014/052865 (2 pages). cited by
applicant .
International Preliminary Report on Patentability dated Mar. 22,
2016, issued in connection with International Application No.
PCT/GB2014/052865 (7 pages). cited by applicant .
European Office Action dated Aug. 10, 2018, issued in connection
with European Application No. 14787014.1 (5 pages). cited by
applicant .
Office Action (Restriction Requirement) dated Feb. 1, 2018, issued
in connection with U.S. Appl. No. 15/023,307 (7 pages). cited by
applicant .
Office Action dated Jul. 6, 2018, issued in connection with U.S.
Appl. No. 15/023,307 (17 pages). cited by applicant .
Office Action dated Jan. 15, 2019, issued in connection with U.S.
Appl. No. 15/023,307 (16 pages). cited by applicant .
Combined Search and Examination Report dated Oct. 24, 2013, issued
by the UK Intellectual Property Office in connection with
Application No. GB1316652.5 (8 pages). cited by applicant .
Search Report dated Nov. 11, 2013, issued by the UK Intellectual
Property Office in connection with Application No. GB1316652.5 (3
pages). cited by applicant .
Examination Report dated Aug. 4, 2016, issued by the UK
Intellectual Property Office in connection with Application No.
GB1316652.5 (3 pages). cited by applicant .
Examination Report dated Jan. 12, 2017, issued by the UK
Intellectual Property Office in connection with Application No.
GB1316652.5 (2 pages). cited by applicant .
European Office Action dated Jul. 16, 2021, issued in connection
with European Patent Application No. 14787014.1 (5 pages). cited by
applicant.
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Primary Examiner: Cohen; Brian W
Attorney, Agent or Firm: McCarter & English, LLP
Parent Case Text
RELATED APPLICATIONS
This application is a divisional of U.S. patent application Ser.
No. 15/023,307 filed on Mar. 18, 2016, which is the 35 U.S.C.
.sctn. 371 U.S. National Phase of International Application No.
PCT/GB2014/052865 filed on Sep. 19, 2014, which claims the benefit
of United Kingdom (Great Britain) Patent Application No. 1316652.5
filed on Sep. 19, 2013. The entire disclosures of the foregoing
applications are incorporated by reference herein.
Claims
The invention claimed is:
1. A method of electrolytic etching and deposition, comprising: a.
introducing a continuous section of substrate into an electrolyte
within a container, wherein the substrate is initially patterned
and includes a conductive layer comprising protected areas defined
by having a patterned layer of protective material formed thereon
and unprotected areas defined by being without a patterned layer of
protective material formed thereon; b. applying a voltage between a
first electrode, in electrical contact with the electrolyte, and a
second electrode, physically separated from the first electrode and
in electrical contact with the substrate, and thereby removing the
unprotected areas of the conductive layer of the substrate by
electrolytic etching; c. removing the patterned layer of protective
material to change the protected areas into further unprotected
areas; and d. at a subsequent time, reversing the polarities of the
first electrode, in electrical contact with the electrolyte, and
the second electrode, in electrical contact with the substrate, and
thereby increasing the thickness of the further unprotected areas
of the conductive layer of the substrate by electrolytic
deposition.
2. The method of claim 1, wherein the second electrode is in
electrical contact with the substrate via means for introducing the
continuous section of substrate through the electrolyte.
3. The method of claim 2, wherein the means for introducing the
continuous section of substrate through the electrolyte comprises a
feed roller.
4. The method of claim 1, wherein the first electrode is removable
from the container.
5. The method of claim 4, further comprising removing the first
electrode from the container.
6. The method of claim 1, wherein the container includes a drain
for draining the electrolyte.
7. The method of claim 6, further comprising draining at least some
of the electrolyte using the drain.
8. The method of claim 1, wherein the container includes a guide
for guiding the continuous section of the substrate.
9. The method of claim 8, further comprising guiding the continuous
section of the substrate through the container using the guide.
10. The method of claim 1, further comprising one or more of: means
for storing and dispensing the substrate, means for laminating the
substrate, means for printing the substrate, means for optical
inspection of the substrate, means for photolithography of the
substrate, means for drying the substrate, means for developing the
substrate, and means for washing the substrate.
11. The method of claim 1, wherein at least some of the material
that is removed from the substrate during the step of electrolytic
etching is re-deposited onto the conductive layer of the substrate
during the step of increasing the thickness of the conductive layer
of the substrate by electrolytic deposition.
12. The method of claim 11, wherein the at least some of the
material that is removed from the substrate during the step of
electrolytic etching was deposited onto the first electrode, and is
re-deposited onto the conductive layer from the first electrode.
Description
FIELD OF THE INVENTION
The present invention relates to the fabrication of electronic
circuits and/or semiconductors on flexible substrates.
BACKGROUND OF THE INVENTION
As is known in the art, fabrication of circuitry usually involves
the stages of deposition, removal, patterning and modification of
electrical properties. This process has been streamlined with the
introduction of reel-to-reel production for flexible substrates.
Further to this, reel-to-reel fabrication processes are known in
which an element of the process uses electrolysis, specifically
electroplating of the conductive layers of substrates.
US 2012/0305892 is concerned with an electronic device comprising
an in-plane component formed in an organic semiconductor layer,
desirably graphene, on a flexible substrate, wherein the component
is formed using imprint lithography to create a trench through the
organic semiconductor layer in a roll-to-roll process, wherein the
number of process steps required is limited to allow manufacture of
the device in a single integrated apparatus.
US 2004/0259365 is concerned with providing a polishing method and
a polishing apparatus for appropriately controlling the potential
of an acting electrode to perform an accurate and stable
electrolytic polishing process; there is also provided a method of
manufacturing a semiconductor device using the polishing method and
the polishing apparatus.
In the past, using electrolysis in the fabrication of electronic
circuits and/or semiconductors has been difficult to practically
achieve. Specifically, it has been difficult to achieve a system
design where an electrical voltage is applied to the conductive
elements of the substrate. Further, in systems where the desired
connection has been achieved, it has previously been at the expense
of the speed and thereby efficiency of the continuous processing of
the system, for instance requiring a separate stage in the
fabrication process, where no other processing is able to be
undertaken, wherein the substrate is held stationary and an
electrode is steadily moved towards the substrate, thereby applying
a voltage to the substrate.
As such, it would be beneficial in the field if a system design
were envisaged in which the application of the voltage to the
substrate, that is turning the substrate into an electrode, were
seamlessly integrated into the fabrication process in a manner that
required no extra stages and no further time delay when added to
the usual operation processes of the fabrication system. Stated
another way, a system of such a design would represent a saving of
time, and thereby an increase in efficiency, over current
fabrication processes that include an electrolysis stage.
Manufacturers are ever more concerned with the impact that their
processes may be having on the environment around them. However, it
is crucial that such concerns can be addressed within the context
of profitable business. As such, innovations that can
simultaneously decrease the adverse effects on the environment,
whilst also increasing efficiency, represent vital contributions to
the field.
STATEMENT OF THE INVENTION
The aspects of the present invention are defined by the
accompanying claims.
According to one embodiment of the present invention, there is
provided a means for the fabrication of flexible conductive
circuitry within a reel-to-reel production process.
BRIEF DESCRIPTION OF THE DRAWINGS
There now follows, by way of example only, a detailed description
of preferred embodiments of the present invention, with reference
to the figures identified below.
FIG. 1 is a schematic cross-section of the apparatus in
operation.
FIG. 2 is a schematic cross-section of the laminator unit, optical
inspection unit and photolithography unit.
FIG. 3 is a schematic cross-section of any one of the photoresist
development unit, the post-development wash unit, the post-etch
wash unit or the photoresist removal unit.
FIG. 4 is a schematic cross-section of the conductive-layer etch
unit.
FIG. 5 illustrates a section of the substrate.
FIG. 6 illustrates a section of the substrate which has a patterned
layer of material formed on the conductive side of the
substrate.
FIG. 7 illustrates the action of the electrolytic process on both
the section of substrate and the electrode.
FIG. 8 illustrates a section of the substrate after the fabrication
process.
FIG. 9 illustrates a process of redeposition.
FIG. 10 illustrates alternative components to be used in the
fabrication process.
FIG. 11 illustrates the alternative embodiment of the fabrication
process using the components of FIG. 10.
DETAILED DESCRIPTION OF THE EMBODIMENTS
In the following description, functionally similar parts carry the
same reference numerals between figures.
The present invention comprises a system for the production of
electronic circuits or semiconductors onto flexible substrates. In
particular, the system is an inline system, known in the art as
reel-to-reel, whereby the process of fabrication can be said to be
continuous.
FIG. 1 illustrates a cross-section of the apparatus in operation.
The system has a laminator unit 1 that forms a substrate 2. The
substrate 2 exits the laminator unit 1 and is transported towards
the photolithography unit 6, and in doing so passes an optical
inspection unit 4. The substrate 2 is then transported to the
photoresist development unit 8, before being further transported to
the post-development wash unit 10. Following this, the substrate 2
is transported to the conductive-layer etch unit 12, and
subsequently the post-etch wash unit 14. Finally, the substrate 2
is transported to the photoresist removal unit 16, after which the
substrate has been successfully fabricated in preparation for the
addition of electronic devices or constructs. The operation of the
individual units of the system will be further described below.
As an illustrative example, the conductor-coated substrate
described herein is most frequently referred to as ITO coated PET,
however those skilled in the art will appreciate that this material
could be any transparent or non-transparent material such as one or
more of ITO, ATO, gold, silver graphite, copper, graphene, zinc
oxide, aluminium oxide, lead zirconium titanate, barium titanate
and any other appropriate coating that can be deposited on the
substrate in a thin layer. The material may be provided in one or
more continuous or semi-continuous conductive coating or layer, and
may comprise a plurality of such layers of the same or different
materials, such as the materials mentioned above. Similarly, the
substrate can be any material that can be coated with a thin layer
of conductive material, and in some cases the conductive material
itself may also act as the substrate.
FIG. 2 illustrates a cross-section of the laminator unit 1, optical
inspection unit 4 and photolithography unit 6. The laminator 1 has
a substrate feed roller 18, which inputs the substrate base layer
19 into the system. Similarly, the dry etch resist feed roller 20
inputs the dry etch resist layer 21 into the system. The pressure
and traction roller 22 operates in conjunction with the heated
pressure roller 24 to output the substrate 2 to the alignment
rollers 26 at the exit of the laminator unit 1.
The photolithography unit 6 has variable height rollers 30,
supported by variable height roller support arms 36, positioned at
its entrance and exit. Within the photolithography unit 6 is a
pattern design 32, which is illuminated by an array of Ultra Violet
(U.V.) light sources 28.
In operation, the laminator unit 1 is designed to physically
combine the constituent materials of a flexible substrate. This is
achieved in a uniform manner through the application of heat and
pressure. To avoid contamination by external elements, the
laminator unit 1 is both light-sealed and dust-sealed, thereby
protecting the light-sensitive materials contained within. The
laminator unit 1 is designed to accommodate separate rolls for each
of the constituent materials of a flexible substrate within it. For
instance, the material that is to be used as the substrate base
layer 19 would be fitted as a roll onto the substrate base feed
roller 18. Similarly, the material to be used as the dry etch
resist layer 21 would be fitted as a roll onto the dry etch resist
feed roller 20. The material that is to be used as the substrate
base layer 19 may be coated with a transparent conductive material
or materials such as mentioned above. However, as will be
appreciated by those skilled in the art, the coating of the
substrate base layer 19 does not have to be transparent, and the
substrate itself can be any material that can be dispensed from as
roll. Further, in some cases, the conductive material may itself
form the substrate base layer 19. When activated, the laminator
unit 1 would act to simultaneously unwind the substrate base feed
roller 18 and the dry etch resist feed roller 20, at a synchronized
speed, ensuring that the rolls remain both wrinkle and air-bubble
free. This action would feed both the substrate base layer 19 and
the dry etch resist layer 21 towards the pressure and traction
roller 22 and the heated pressure roller 24. The substrate base
layer 19 and the dry etch resist layer 21 intersect at a point
directly between the pressure and traction roller 22 and the heated
pressure roller 24. At this intersection, the pressure and traction
roller 22 applies a lateral force from its surface into the
substrate 2 along a plane perpendicular to the surface of the
substrate 2. Simultaneously, the heated pressure roller 24 applies
both heat, and a lateral force from its surface into the substrate
2 along a plane parallel, but oppositely directed, to the force
applied by the pressure and traction roller 22. In this manner, the
simultaneous action of the heat and pressure application acts to
physically combine the substrate base layer 19 and the dry etch
resist layer 21 into a single flexible substrate 2, suitable for
undergoing etching for the purpose of electronic circuit and/or
semiconductor fabrication. Following this, the laminator unit 1
outputs the newly formed substrate 2 through the alignment rollers
26, which are able to move along the vertical axis, and thereby act
to correctly orientate the substrate 2 for the optical inspection
process.
The substrate 2 is outputted from the laminator unit 1 towards the
photolithography unit 6 along a path 34. Before entering the
photolithography unit 6, the substrate 2 is subjected to an
inspection for defects by an optical inspection unit 4. For
instance, the optical inspection unit 4 could comprise a camera
system connected to a processor that is configured to inspect the
substrate 2 for visible defects following the lamination process of
the laminator unit 1. Typical defects of interest include, but are
not limited to, bubbles, wrinkles, creases, rips and overlaps, as
well as any other marks that could affect the exposure process. In
the event that a defect is located by the optical inspection unit
4, the processor system will notify the operator and the substrate
2 will be moved past the area of defect, thus ensuring only
substrate that is not defected will continue to be processed by the
setup as disclosed. This has the advantageous effect of efficiently
implementing resources, where no further processing in the
production line is wasted on defective elements of the substrate,
thereby saving electrical power, time and chemical resources.
Following optical inspection, the substrate 2 will be transported
along substrate path 34 into the photolithography unit 6 by the
rotation of the adjustable height rollers 30, which also serve to
maintain a constant tension across the substrate 2. The substrate 2
will follow substrate path 34 until it is correctly positioned over
the pattern design 32, which is fixed in location within the
photolithography unit 6. Once in location above the pattern design
32, the adjustable height roller support arms 36 will retract
downwards, moving the adjustable height rollers 30 similarly
downward, thereby pulling the substrate 2 into contact with the
pattern design 32. The pattern design 32 is a pattern formed by the
relative positioning of areas that are opaque, to areas that are
transparent, and is arranged to form the design of the desired
final circuitry. With the substrate 2 now in contact with the
pattern design 32, the U.V. light source array 28 is automatically
activated for a certain predetermined period of time, thereby
illuminating the areas of the photoresist layer of the substrate
that are left exposed by the transparent areas of the pattern
design 32. By chemical processes known in the art, the areas of the
photoresist layer of the substrate 2 that are illuminated by the
U.V. light source array 28 will undergo chemical changes in their
material properties, leaving these areas markedly altered in
comparison with the areas of the photoresist layer which were
unexposed to the U.V. light. After the illumination is completed
and the pattern has been transferred, the adjustable height roller
support arms 36 will extend upwards, in turn moving the adjustable
height rollers 30, thereby taking the substrate 2 and the pattern
design 32 out of contact. Following this, the adjustable height
rollers 30 will rotate so as to transport the substrate 2 out of
the photolithography unit 6 along substrate path 34.
The process as described above has been described within the
context of a specific example, namely that of positive
photolithography. However, as will also be appreciated by those
skilled in the art, the apparatus disclosed in FIG. 2 could equally
be used with, for instance, negative photolithography, or other
types of photolithography not herein described.
FIG. 3 is an illustrative cross-section of any one of the
photoresist development unit 8, the post-development wash unit 10,
the post-etch wash unit 14 or the photoresist removal unit 16.
Whilst the function of each of these units within the fabrication
process is different, the design of the apparatus required to
perform these functions is substantially the same, with only the
chemical composition of the fluid 42 and the varying methods of
operation being different. In order to function effectively, each
tank 46 is both electrochemical and solvent resistive, and is
preferably, but not essentially, transparent for the purpose of
inspection. Within each tank 46 there is contained a fluid 42,
through which the substrate 2 travels along the substrate guide 40.
To effect this movement, there are current carrying traction feed
rollers 38 placed at the entrance of each tank 46, which are
connected to an electrical power source (not shown) by electrical
connectors 44, and traction feed rollers 54 placed at the exit of
each tank 46, wherein the current carrying traction feed rollers 38
are used to ensure that an electrical current is always present in
the substrate 2. As the fabrication process herein described
comprises a plurality of the tank units shown in FIG. 3, each unit
in the system is in electrical contact by virtue of the substrate
2. Hence, as certain tank units, namely the conductive-layer etch
unit 12 of FIG. 4, involve the application of voltages in their
operation, it is thereby necessary to apply voltages to the
remaining tank units in the system to directly oppose and thereby
neutralize the voltages that may leak from the conductive-layer
etch unit 12 into units of the system that do not require
electrical current in their operation. This is the purpose of the
current carrying traction feed rollers 38. The tank 46 also has a
cap 52 for refilling the fluid 42, and a drain plug 50 for draining
the fluid 42 from the tank 46. Also within the tank 46 is a
substrate guide roller 48, and an aeration system 56 placed on each
interior wall of the tank 46. In an alternative embodiment, the
tank 46 may contain a plurality of substrate guide rollers 48, of
substantially similar structure but varying size, which would
enable the processing of longer sections of substrate 2. In a
further alternative, the traction feed roller 54 may be
electrically connected, for example to collect digital reference
information used to reference the location of the substrate 2
within the process.
In operation, the photoresist development unit 8 transports the
substrate 2 into the entrance of the unit through the rotation of
the current carrying traction feed rollers 38. The electrical
connectors 44 provide an electrical voltage to the current carrying
traction feed rollers 38, which serves to oppose and neutralise any
voltages that may propagate along the substrate 2 from other units
in the system. On entering the tank 46, the substrate 2 further
enters a substrate guide 40. The substrate guide 40 can be imagined
to be physically and functionally similar to the guide tracks that
a sliding door moves along, as the substrate guide 40 merely
brackets the sides of the substrate, leaving the top surface and
bottom surface exposed to the fluid 42. As can be seen in FIG. 3,
the substrate guide 40 traverses the full length of the tank,
taking the substrate 2 through a large volume of the fluid 42. The
substrate 2 is pulled through the fluid 42 through the rotational
traction of the substrate guide roller 48 until such time as the
current carrying traction feed roller 38 comes into contact with a
conductive area of the substrate 2 where there is no photoresist
present, at which point the system sensors (not shown) detect that
the substrate 2 is in the correct position, and the transportation
of the substrate 2 is stopped.
As this is the photoresist development unit 8, the fluid 42 in this
case is a fluid suitable for developing the photoresist layer that
was subjected to UV light exposure in the photolithography unit 6,
and will be known by those skilled in the art. By virtue of the
chemical change that the areas of the substrate 2 that were exposed
to UV light in the photolithography unit 6 underwent, the
developing fluid acts to chemically dissolve the photoresist layer
of these areas, creating a suspension of the dissolved material in
the fluid 42. This process of development is aided by the
introduction of air bubbles into the tank 46 from the aeration
system 56, which in acting like a physical stirrer serves to
agitate the fluid sufficiently to increase the molecular reaction
rate of the developing fluid on the photoresist layer of the
substrate 2. This process leaves the top layer of the substrate 2
only bearing the photoresist layer that was intended by the design.
After the substrate 2 has moved through the tank 46, the traction
feed rollers 54 transport the substrate through the exit of the
photoresist development unit 8 along path 34. Following the use of
the photoresist development unit 8, when the setup is no longer in
use, it is possible to drain the fluid 42 from the tank 46 by means
of the drain plug 50. This leads to the advantageous effect of
being able to reclaim the material that formerly comprised the
photoresist layer of the substrate 2 that was dissolved by the
fluid 42 during the development process. In this way the design can
be seen to reduce the cost of materials in the process, and can
thereby also be considered to be environmentally friendly. Before
operation is intended to begin again, the fluid can be refilled
through cap 52. This embodiment could be used in processes where
any other element of the substrate were to be removed (as opposed
to just those which were exposed to UV light), requiring only that
in such instances a photoresist appropriate for such a process has
been used.
In operation, the post-development wash unit 10 is substantially
similar to the photoresist development unit 8 described above. In a
fashion similar to that described above, the substrate 2 having
been processed by the photoresist development unit 8 then enters
the post-development wash unit 10, and is transported through the
fluid 42. In the case of the post-development wash unit 10, the
fluid 42 contained within is a fluid suitable for the cleaning of
the substrate 2, removing and neutralising any traces of developing
fluid that may have remained on the substrate 2 following the
operation of the photoresist development unit 8. Further, the
action of the cleaning fluid also removes any further remnants of
the photoresist layer that were intended to be removed in the
photoresist development unit 8. In a similar manner to that of the
photoresist development unit 8, the fluid can be drained through
drain plug 50, and any materials in suspension can be reclaimed for
reuse.
FIG. 4 is a schematic cross-section of the conductive-layer etch
unit 12. The design of the conductive-layer etch unit 12 is similar
to the design of the tank of FIG. 3; however there are some
essential features of distinction. The underlying feature that
drives this distinction is that the conductive-layer etch unit 12
is designed to exploit the phenomenon of electrolysis. In line with
this operation, an electrode 58 is attached to the cap 52, which
projects downwards and into the fluid 42. This electrode is
provided with a DC electrical voltage of a particular polarity by
the electrical connector 60. The electrode of opposite polarity is
physically separated from the first electrode 58, and is here
advantageously incorporated into the functionality of the
electrically polarized traction feed roller 55. The electrically
polarized traction feed roller 55 is provided with a DC voltage of
a polarity opposite to the electrode 58, by means of the electrical
connector 62. In comparison with the setup of FIG. 3, the other
distinction to be made is the lack of aeration system 56. These
important differences aside, the form of the tanks are
substantially similar.
In operation, the conductive-layer etch unit 12 of FIG. 4 pulls the
substrate along path 34 and into the tank 46 by means of the
electrically polarized traction feed rollers 55. Following the
processes of the previous stages, the substrate 2 arrives at the
electrically polarized traction feed rollers 55 with select areas
of the conductive layer exposed. As such, when the substrate 2
comes into contact with the electrically polarized traction feed
rollers 55, the electrical voltage as supplied by electrical
connector 60 imparts a current of the same polarity into the
conductive layer of the substrate 2. The substrate 2 then proceeds
towards the fluid 42 by means of the rotation of the substrate
guide roller 48. The tank 46 contains an electrolyte that is known
in the art. As would be appreciated by the person skilled in the
art, this fluid should also be suitable for use with the conductive
compound to be removed from the substrate 2, as would be
appropriate for an electrolytic process. The substrate 2 is brought
into the fluid 42, whereby the process of electrolysis begins due
to the electrical current flowing into the fluid 42 from the
electrode 58. Unlike conventional electrolytic processes within the
art of conductive circuit fabrication, the process disclosed herein
is that of electrolytic etching, whereby the flow of material is
from the substrate 2 to the fluid 42, thereby removing material
from the surface of the substrate 2. As such, upon entering the
fluid 42, the conductive layer of the substrate 2 will be
electrically driven, by virtue of the potential difference created
between the electrode 58 and the conductive layer of the substrate
2 from the electrically polarized traction feed roller 55, to give
up ions to constitute a flow of current through it. In this way,
the conductive layer will be gradually, but continually, depleted
of its conductive layer until the entire conductive layer is
removed and charge ceases to flow, at which point the system
sensors (not shown) will deem the process complete. At this point,
the system sensors (not shown) detect that current is no longer
flowing within the conductive-layer etch unit 12, and the substrate
2 is transported out of the tank 46 by the usual action of the
traction feed rollers 54 as described previously. Alternatively,
only part of the conductive layer may be removed, and the
electrolytic etching may be halted after a predetermined time or on
detection of a predetermined condition. The current or voltage may
be varied so as to control the rate of electrolytic etching.
Following this process, at a time when the system is not in use,
the electrode 58 can be removed, and the conductive material that
has been deposited on it by the process of electrolysis can be
disposed of safely or recycled. In this way, an extremely high
percentage of the material removed can be collected and reused. In
the case of the system as described above the electrolytic compound
is oxalic acid highly diluted with ionized water, however those
skilled in the art will appreciate that the setup allows for the
use of any other appropriate substance.
Referring to FIG. 3, in operation, the post-etch wash unit 14 is
substantially similar to the post-development wash unit 10
described above. In a fashion similar to that described previously,
the substrate 2 having been processed by the conductive-layer etch
unit 12 then enters the post-etch wash unit 14, and is transported
through the fluid 42. In the case of the post-etch wash unit 14,
the fluid 42 contained within is a fluid suitable for the cleaning
of the substrate 2, removing and neutralising any traces of etching
fluid that may have remained on the substrate 2 following the
operation of the conductive-layer etch unit 12. Further, the action
of the cleaning fluid also removes any further remnants of the
conductive layer that were intended to be removed in the
conductive-layer etch unit 12. In a similar manner to that of the
post-development wash unit 10, the fluid can be drained through
drain plug 50, and any materials in suspension can be reclaimed for
reuse.
Referring to FIG. 3, in operation, the photoresist removal unit 16
is substantially similar to the photoresist development unit 8
described above. In a fashion similar to that described previously,
the substrate 2 having been processed by the post-etch wash unit 14
then enters the photoresist removal unit 16, and is transported
through the fluid 42. In the case of the photoresist removal unit
16, the fluid 42 contained within is a fluid suitable for the
removal of the final layer of the photoresist that is still present
on the substrate 2. This fluid will act to chemically dissolve the
final remaining layer of photoresist that is present on the
substrate 2, after which only the conductive layer in the design of
the intended circuit, as applied in the photolithography unit 6,
remains on the surface of the substrate 2. This process leaves the
removed photoresist layer in suspension in the fluid 42. In a
similar manner to that of the post-development wash unit 10, the
fluid can be drained through drain plug 50, and any materials in
suspension can be reclaimed for reuse. In a similar manner to that
of the photoresist development unit 8, the fluid can be drained
through drain plug 50, and any materials in suspension, such as the
removed photoresist, can be reclaimed for reuse.
In the embodiments described above, the fabrication process has
been demonstrated in the context of discontinuous movement of the
substrate 2 through the system, wherein at certain points the
substrate is held in place whilst processing is completed. However,
it will be appreciated that further embodiments, not included for
conciseness, could be envisaged where the motion of the substrate 2
is continuous throughout the system.
FIGS. 5 to 8 demonstrate the appearance of the flexible substrate
at various stages in the fabrication process described above.
FIG. 5 illustrates a section of ITO coated PET 64 that can be used
in the above embodiments. However, as is true for all of the
embodiments herein, this material could be any transparent or
non-transparent material with a continuous or semi-continuous
conductive coating, such as described above. Similarly, the
substrate can be any material that can be coated with a thin layer
of conductive material, and in some cases the conductive material
itself may also act as the substrate.
FIG. 6 illustrates a section of ITO coated PET 64, as in FIG. 5,
which has a patterned layer of protective material 66 formed on the
conductive side of the substrate to protect select areas of the
conductive layer from being removed when it is subjected to the
patterning process described in earlier embodiments. This is how
the substrate appears on leaving the photoresist development unit
8, and also how it appears after washing in post-development wash
unit 10 before entering conductive-layer etch unit 12. Any
substance that is used in the patterning process must not remove
the protective material layer 66, as this would result in damage to
the electronic circuit, as well as the partial or complete removal
of sections that are not desired to be removed.
FIG. 7 illustrates a section of ITO coated PET where the ITO that
is not protected has migrated (represented by dashed arrows) from
the surface of the PET to the electrode 58 in the manner previously
described in relation to the electrolytic action of the
conductive-layer etch unit 12. This migration of ITO results in the
electrode 58 being covered by a deposited layer of ITO 68.
Advantageously, almost all of the ITO that is removed from the PET
during this process can be reused in further processes, as will be
described below.
FIG. 8 illustrates a section of ITO coated PET where the protective
coating 66 has been removed revealing the desired pattern of
conductive material 70. This is how the final substrate
appears.
FIG. 9 illustrates a process of electroplating redeposition (82)
that is an advantageous addition to the fabrication process
described herein. This advantageous addition is only possible due
to the distinguishing processes and embodiments described herein,
which as previously stated, is unlike conventional electrolytic
processes within the art of conductive circuit fabrication as the
process disclosed is that of electrolytic etching, whereby the flow
of material is from the substrate 2 to the fluid 42, thereby
removing material from the surface of the substrate 2. As a result
of this action, as previously described in relation to the
conductive-layer etch unit 12, there is a significant quantity of
the conductive layer of the substrate 2 deposited on the electrode
58. The setup disclosed in FIG. 9 seeks to advantageously exploit
this feature.
In operation, the setup of FIG. 9 is envisaged to occur within a
tank called the redeposition tank, that is substantially similar in
design to the conductive-layer etch unit 12 of FIG. 4. A section of
ITO coated PET is shown, where the ITO that is collected on the
electrode 68 is to be deposited back onto the already patterned ITO
by reversing the polarity of the electrical field as previously
described in relation to conductive-layer etch unit 12. As such,
the polarity of the field between the electrode 58 and the
remaining ITO on the PET substrate 2, as effected by electrically
polarised traction feed rollers substantially similar those number
55 in FIG. 4, will be reversed. This reversal in polarity of field
will have the opposite effect of the electrolytic process described
in relation to FIG. 4, namely the conductive material deposited on
the electrode 68 will be driven to give up ions to constitute a
reverse flow of current whereby the conductive material ends up
being redeposited onto the conductive ITO that is left on the PET
substrate. This results in a substantially thicker layer of
conductive material 72 on the substrate 2. As the current continues
to flow, redeposition will continue to occur until a state is
reached that is deemed to be sufficient by the system sensors (not
shown). The current or voltage may be controlled so as to control
the thickness of the redeposited material. Preferably, the applied
voltage or current is DC (Direct Current) and the reversal of
polarities occurs between discrete steps of the deposition
process.
This setup solves a number of problems, and thus represents a
number of advantageous effects. Firstly, it is often in the
manufacturer's interest to have a thin conductive layer on the
substrate, as this is faster to remove during fabrication. However,
less conductive material makes for a much less efficient conductive
surface, and subsequently a less efficient electronic circuit. This
redeposition of conductive material onto the already present
conductive material solves this problem, as in many cases a
substantial amount of the conductive material needs to be removed
or disconnected from the substrate to get the pattern required, and
so being able to reuse this conductive material by redeposition
represents a significant advantageous increase in the conductivity,
efficiency and durability of the resulting electronic
substrate.
Secondly, as the conductive material constitutes the most expensive
component of the substrate, the ability to recycle and redeposit it
represents a significant advantageous saving in cost.
This process can be implemented with the previous embodiments of
the disclosure in a number of manners. For instance, a setup as
seen in FIG. 1 can be envisaged whereby following the photoresist
removal unit 16 there is a redeposition tank substantially similar
to the conductive-layer etch unit 12, where in operation the
electrode is mechanically moved (by machinery not shown here)
between the conductive-layer etch unit 12 and said redeposition
tank to alternately remove and collect the conductive layer
material during the etching process at conductive-layer etch unit
12, and then deposit the collected conductive layer back onto the
substrate in said redeposition tank. Alternatively, a setup could
be envisaged where computer systems (not described here) could be
used reverse the direction of the substrate through the system,
wherein an area of substrate having been through the entire
fabrication process up to immersion in the photoresist removal unit
16, could then be realigned into the conductive-layer etch unit 12,
which then has its electrical polarity reversed relative to its
original operation, thereby constituting a redeposition of
conductive material as previously described. For this system to
work, it is evident that the nature of the chemicals chosen to be
used in each of the tank units need to be of a type that does not
in any way damage or effect the state of the substrate when the
system is run in reverse, where the substrate moves backward
through tanks by which it has already been processed. The person
skilled will appreciate this and be able to achieve a suitable
setup using known methods.
These exemplary embodiments are to be seen as merely illustrative
and not limiting of the manner in which the setup of FIG. 9 could
be implemented within the fabrication process as disclosed herein.
It will be appreciated that further embodiments, not included for
conciseness, could be envisaged.
FIG. 10 illustrates an alternative embodiment in which the
laminator unit 1 and the photolithography unit 6 of all previous
embodiments are replaced by alternative units, as described below.
The replacement of these two units by alternative units is the only
distinction over the previous embodiments, and so it can be seen
that these two units can merely be combined with all previously
disclosed embodiments in place of the laminator unit 1 and the
photolithography unit 6. A roll of PET coated with ITO 74 is
positioned in such a way such that the substrate 2 is in a location
that is advantageous to the dispensing of the material. An inkjet
printer 76 is supplied with the pattern that is to be made on the
substrate (in a process known in the art and not described here).
The optical inspection unit 4 is identical in form and function to
that previously described. An Infra-Red (IR) drying unit 78,
containing multiple IR sources 80, is used to fix the ink that has
been dispensed by the printer (in a process known in the art and
not described here). The inkjet printer 76 may be replaced by an
inline silk screen printer, a flexographic printer or any other
printing possesses that are able to dispense the type of material
used as a protection layer for the conductive material.
FIG. 11 is an illustration of the fabrication system using the
alternative components as shown in FIG. 10 and described above.
ALTERNATIVE EMBODIMENTS
The embodiments described above are illustrative of, rather than
limiting to, the present invention. Alternative embodiments
apparent on reading the above description may nevertheless fall
within the scope of the invention.
REFERENCE NUMERALS
TABLE-US-00001 1 - laminator unit 2 - substrate 4 - optical
inspection unit 6 - photolithography unit 8 - photoresist
development unit 10 - post-development wash unit 12 -
conductive-layer etch unit 14 - post-etch wash unit 16 -
photoresist removal unit 18 - substrate base feed roller 19 -
substrate base layer 20 - dry etch resist feed roller 21 - dry etch
resist layer 22 - pressure and traction roller 24 - heated pressure
roller 26 - alignment rollers 28 - U.V. light source array 30 -
adjustable height rollers 32 - pattern design 34 - substrate path
36 - adjustable height roller support arm 38 - current carrying
traction feed rollers 40 - substrate guide 42 - process-specific
fluid 44 - electrical connectors 46 - tank (electrochemical and
solvent resistive) 48 - substrate guide roller 50 - drain plug 52 -
cap 54 - traction feed roller 55 - electrically polarised traction
feed roller 56 - aeration system 57 - traction feed rollers 58 -
electrode 60 - electrical connector 62 - electrical connector 64 -
ITO coated PET 66 - protective material layer 68 - deposited layer
of ITO 70 - desired pattern of conductive material 72 - thick layer
of redeposited conductive material 74 - substrate roll 76 - inkjet
printer 78 - IR drying unit 80 - IR sources 82 - electroplating
redeposition
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